Method for transmitting information in a mimo radio communication system and radio communication system

ABSTRACT

A method is provided for transmitting information in a radio communication system provided with at least one transmitting station (AP) and at least two receiver stations (MT). The transmitting station (AP) and the receiver stations (MT) are connected together via a radio communication interface. The transmitting stations (AP) includes a transmitting antenna with K&lt;SB&gt;B&lt;/SB&gt; 3 1 antenna elements, whereby K&lt;SB&gt;B&lt;/SB&gt;≧1, and the receiving stations (MT) respectively include a transmitting antenna with K&lt;SB&gt;M&lt;/SB&gt; antenna elements, whereby K&lt;SB&gt;M&lt;/SB&gt;≧1, and which communicate via a MIMO-transmission. The transmitting signals transmitted from the antenna elements of the transmitting antenna of the transmitting station (AP) are produced in a common process and are adapted in relation to the transmitting energy to be used during radiation. Receiving signals received by the antenna elements of the receiver antenna of the receiver stations (MT) are detected in a linear signal process.

BACKGROUND OF THE INVENTION

In a radio communication systems, information (for example speech, imageinformation, video information, SMS (Short Message Service) or otherdata) is transmitted using electromagnetic waves over a radio interfacebetween transmitting and receiver stations (base station or subscriberstation). In such cases, the electromagnetic waves are propagated usingcarrier frequencies lying within the frequency band provided for therelevant system. For the GSM (Global System for Mobile Communication)mobile radio system which has been introduced, frequencies at 900, 1800und 1900 MHz were used. For future mobile radio systems with CDMA orTD/CDMA procedures, such as UMTS (Universal Mobile TelecommunicationSystem) or other third-generation systems, there is provision forfrequencies in the frequency band of around 2000 MHz.

The access from stations to the shared transmission medium is regulatedin these radio communication systems by Multiple Access (MA). With thesemultiple accesses, the transmission medium can be subdivided between thestations in the time area (Time Division Multiple Access, TDMA), in thefrequency area (Frequency Division Multiple Access, FDMA), in the codearea (Code Division Multiple Access, CDMA) or in the space area (SpaceDivision Multiple Access, SDMA). In this case, the transmission medium(with GSM (Global System for Mobile Communications), TETRA (TerrestrialTrunked Radio), DECT (Digital Enhanced Cordless Telecommunication), UMTS(Universal Mobile Telecommunication System) for example) is frequentlysubdivided in the frequency and/or time channels in accordance with theradio interface. These channels are generally referred to astransmission channels or radio channels. For systems where coordinationis decentralized, measurements are used to decide on the usability ofthese transmission channels. In accordance with the radio radiation(i.e., depending on the radio field attenuation), re-use of thesetransmission channels at an appropriate spacing is possible.

For radio transmission between a transmit station and at least onereceiver station of a radio transmission system, interferenceoccurrences now arise as a result of the frequency selectivity of thetransmission channels, such interference being known as intersymbolinterference and Multiple Access interference. The greater thetransmission bandwidth of the transmission channel, the more theseinterferences distort the transmit signals.

Conventionally, the transmit signals are generated at the transmitstation without taking account of the effective radio channels. Theinterference occurrences then arising are rectified in a second step, atleast approximately by the appropriate matched and generally veryexpensive methods for detecting the transmitted data at the receiverstations.

Radio communication systems with at least one transmit station (Transmitstation AP or base station) and at least two receiver stations (Receiverstation MT) are known, with the transmit station (AP) and the receiverstations (MT) being connected to one another over a radio communicationsinterface. Here, the transmit station features a transmit antenna withK_(B) antenna elements (with K_(B)≧1) and the receiver stations eachfeature a transmit antenna with K_(M) antenna elements (with K_(M)≧1).They communicate by MIMO (Multiple Input-Multiple Output) transmission.

Radio transmission devices with at least one transmit station having anumber of transmit elements and with at least one receiver stationhaving a number of receive elements are referred to in this document asMIMO systems. Radio transmission between at least one transmit stationand at least one receiver station of a MIMO system is subject, as aresult of the frequency selectivity of the transmission channels, tointerference occurrences which are known as intersymbol interferencesand Multiple Access interference. For the purposes of radio transmissionfrom at least one transmit station to the receiver stations in a MIMOthere are basically two requirements which need to be fulfilled:

-   -   suitable transmit signals are to be generated and propagated by        the relevant transmit station for each of the transmit antennas;        and    -   the data which is of interest in each case is to be detected by        each of the receiver stations by suitable processing of the        receive signals of all receive antennas.

In recent years, alternative concepts, such as Joint Transmission orJoint Predistortion have been investigated, which, by taking account ofthe effective transmission channels, eliminate the interferenceoccurrences completely, to a large extent or at least partly at thepoint at which the transmit signals are being generated at the transmitstation. See, for example:

-   -   M. Meurer, P. W. Baier, T. Weber, Y. Lu, A. Papathanassiou,        “Joint Transmission, an advantageous downlink concept for CDMA        mobile radio system using time division duplexing”, IEE        Electronics Letters, Bd. 36, 2000, S. 900-901 [1] and    -   P. W. Baier, M. Meurer, T. Weber, H. Tröger, “Joint Transmission        (JT), an alternative rationale for the downlink of time division        CDMA using multi-element transmit antennas”, Proc. IEEE 7th        International Symposium on Spread Spectrum Techniques &        Applications (ISSSTA'2000), Parsippany/N.J., 2000, S. 1-5 [2].        The cited documents present a Joint Transmission (JT)        transmission method, especially for downlink mobile radio        systems from the base station to the subscriber stations, which        allows simultaneous provision to a number of subscribers. The        transmit signals propagated by the transmit antennas of the base        station or transmit station (AP) are generated in a common        process in this case and optimized with respect to the transmit        energy to be used.

In Joint Transmission systems with at least one transmit station havingat least one transmit antenna and with at least one receiver stationhaving at least one receive antenna, the linear receive-side signalprocessing, referred to below as demodulation, is described by receiverstation-specific demodulator matrices [2].

In conventional Joint-Transmission systems [2], the subscriber-specificdemodulation matrices are defined by fixed signatures; e.g., CDMA codes.This process is particularly determined due to the fact that noinformation about the space and time transmission characteristics of themobile radio channels operating between transmit stations and receiverstations is included in the design of the subscriber-specificdemodulation matrices.

Similar to the process used in the Joint Transmission (JT) method, suchtransmit signals also may be generated when receiver stations with anumber of receive antennas are employed, by using

-   -   information about the effective radio channels and    -   information about the receive-side-specific processing methods        defined a priori for detection,        which, theoretically, perfectly eliminates the interference        occurrences discussed at the point of transmission.

The present invention is, thus, directed toward a method and an improvedtransmit device which, for the effective transmission channels, takesaccount both of a minimization of the transmit power and also of furtherquality criteria, such as a directional characteristic of the transmitsignal for example.

SUMMARY OF THE INVENTION

In accordance with present invention, transmit signals propagated fromthe antenna elements of the transmit station are generated in a commonprocess and matched with regard to the transmit energy to be used forradiation, with the receive signal received by the antenna elements ofthe receive antennas of the receiver station being detected in a linearsignal process.

Advantageously, the individual signals for the antenna elements of thetransmit antenna of the transmit station can be calculated beforeradiation with the aid of a modulator matrix M.

In this case, a transmit signal vector t= M· d can, in particular, begenerated by essentially linear modulation of at least one data vector dto be transmitted with the modulator matrix M.

In a further embodiment of the present invention, demodulation isundertaken with linear receiver-side signal processing, taking accountof the space and time transmission characteristics between transmitstations and receiver stations.

In particular, receive-station-specific demodulator matrices D can beemployed for the linear receive-side signal processing.

Advantageously, each transmit station (AP) and each receiver station(MT) is connected via at least one radio channel characterized by achannel matrix H.

The system matrix B= D· H contained in the modulator matrix M ispreferably given by the product of the demodulator matrix D and channelmatrix H.

With the inventive radio communication system in which the transmitstation features a transmit antenna with KB antenna elements (with KB≧1)and the receiver stations each feature one transmit antenna with KMantenna elements (with KM≧1), parts are provided for generating thetransmit signals propagated from the antenna elements of the transmitantenna of the transmit station (AP) in a shared process and formatching with regard to the transmit energy to be used for radiation, aswell as parts for detecting the receive signals received from theantenna elements of the receive antennas of the receiver stations in alinear signal process.

The radio communication system in accordance with the present inventionis particularly suitable for executing a method in accordance with thepresent invention.

In a Multi-User MIMO transmission system, the present inventioncombines, on the one hand:

-   -   the generation of access-point-specific transmit signals in        accordance with Joint Transmission,        and one the other hand:    -   the demodulation, taking into consideration information about        the space and time division transmission devices, of the        effective mobile radio channels between the transmit stations        and the receiver stations.

Technical implementations of this innovative combined method allow thebenefits of both methods to be profitably employed.

Information about the space and time transmission characteristics of theeffective mobile radio channels between transmit stations and receiverstations can be taken into account when determining theaccess-point-specific demodulation.

Some of the benefits offered by the inclusion of channel characteristicsare as follows:

-   -   Reduction of the total transmit energy,    -   Avoiding combinations of mobile radio channels and incorrectly        matched demodulation matrices,    -   Improvement of the intercell interference situation in cellular        Joint-Transmission systems,    -   Reduction of the SNR degradation (see [3]),    -   Increase in transmission efficiency (see [3]),    -   Increase in system capacity.

More details can be found, for example, in

-   -   H. Tröger, T. Weber, M. Meurer, P. W. Baier, “Performance        Assessment of Joint Transmission (JT) Multi User Downlink with        Multi-Element Transmit Antennas”, European Transmission on        Telecommunications, ETT Vol. 12, No. 5, September/October 2001        [3],

Additional features and advantages of the present invention aredescribed in, and will be apparent from, the following DetailedDescription of the Invention and the Figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a system model of an MIMO JT system in accordance with theinvention.

FIG. 2 shows the structure of a channel matrix H ₀ ^((k)) in accordancewith equation (21) below.

FIG. 3 shows the structure of a channel matrix D ^((k)) in accordancewith equation (38) below.

DETAILED DESCRIPTION OF THE INVENTION

Joint Transmission (JT) is a highly promising transmission method forthe downlink [1, 2, 3] which is proposed for mobile radio systems usingthe hybrid multiple access method TDMA/CDMA. With JT, the transmissionsignals are advantageously generated jointly for all receiver stationsMT. JT is based on prespecified demodulators, wherein on the basis ofthe characteristics of these demodulators and the channel pulseresponses, the modulator in the transmit station AP is defined aposteriori so that intersymbol interference (ISI) and Multiple AccessInterference (MAI) are completely eliminated. To date, investigationsinto JT have only taken account of multi-element antennas at thetransmit station AP. Statistical investigations [3] have revealed thebenefit of transmit antenna groups. The present invention relates to JTfor transmission systems with a number of subscribers, wheremulti-element antennas are used both at the transmit station AP and atthe receiver stations MT. A system model of such a MIMO JT method ispresented below.

Signal Transmission Model of MIMO Systems with a Number of Subscribers

At the AP, a group of K_(B) transmit antenna elements is used and ateach MT μ_(k) k=1 . . . K) a group of K_(M) receive antenna elements isset up. The channel impulse responses

$\begin{matrix}{{{\underset{\_}{h}}^{({k,k_{B},k_{M}})} = \left( {{\underset{\_}{h}}_{1}^{({k,k_{B},k_{M}})}\ldots\mspace{11mu}{\underset{\_}{h}}_{W}^{({k,k_{B},k_{M}})}} \right)^{T}},{k = {1\mspace{11mu}\ldots\mspace{11mu} K}},{k_{B} = {1\mspace{11mu}\ldots\mspace{11mu} K_{B}}},{k_{M} = {1\mspace{11mu}\ldots\mspace{11mu} K_{M}}},} & (1)\end{matrix}$of the dimension W characterize the mobile radio channel between thetransmit antenna element k_(B) and the receive antenna element k_(m) ofMT μ_(k). The transmit antenna-specific transmit signal of dimension S

$\begin{matrix}{{{\underset{\_}{t}}^{(k_{B})} = \left( {{\underset{\_}{t}}_{1}^{(k_{B})}\mspace{11mu}\ldots\mspace{11mu}{\underset{\_}{t}}_{S}^{(k_{B})}} \right)^{T}},{k_{B} = {1\mspace{11mu}\ldots\mspace{11mu} K_{B}}},} & (2)\end{matrix}$is injected into each of the k_(B) transmit antenna elements. The K_(B)antenna-specific transmit signals t ^((k) ^(B) ⁾ from (2) can becombined to form the overall transmit signal

$\begin{matrix}{\underset{\_}{t} = \left( {{\underset{\_}{t}}^{{(1)}^{T}}\mspace{11mu}\ldots\mspace{11mu}{\underset{\_}{t}}^{{(K_{B})}^{T}}} \right)^{T}} & (3)\end{matrix}$of the dimension K_(B)S. With the channel impulse responses h ^((k,k)^(B) ^(,k) ^(M) ⁾ from (1) the MT and antenna-specific channel foldingmatrices

$\begin{matrix}{{{\underset{\_}{H}}^{({k,k_{B},k_{M}})} = \left( {\underset{\_}{H}}_{i,j}^{({k,k_{B},k_{M}})} \right)},{i = {{1\mspace{11mu}\ldots\mspace{11mu} S} + W - 1}},{j = {1\mspace{11mu}\ldots\mspace{11mu} S}},{{\underset{\_}{H}}_{i,j}^{({k,k_{B},k_{M}})} = \left\{ {{{\begin{matrix}{\underset{\_}{h}}_{i - j + 1}^{({k,k_{B},k_{M}})} & {{1 \leq {i - j + 1} \leq W},} \\0 & {{sonst},}\end{matrix}k} = {1\mspace{11mu}\ldots\mspace{11mu} K}},{k_{B} = {1\mspace{11mu}\ldots\mspace{11mu} K_{B}}},{k_{M} = {1\mspace{11mu}\ldots\mspace{11mu} K_{M}}},} \right.}} & (4)\end{matrix}$can be formed. h ^((k,k) ^(B) ^(,k) ^(M) ⁾ of (4) has the dimension(S+W−1)×S.

With t ^((k) ^(B) ⁾ of (2) and h ^((k,k) ^(B) ^(,k) ^(M) ⁾ of (4) thesignal received at the receive antenna k_(M) from MT μ_(k) can beexpressed as vector

$\begin{matrix}\begin{matrix}{{\underset{\_}{r}}^{({k,k_{M}})} = {\sum\limits_{k_{B} = 1}^{K_{B}}{{\underset{\_}{H}}^{({k,k_{B},k_{M}})}{\underset{\_}{t}}^{(k_{B})}}}} \\{= {\underset{\underset{\;^{{\underset{\_}{H}}^{({k,k_{M}})}}}{︸}}{\left( {{\underset{\_}{H}}^{({k,1,k_{M}})}\ldots\mspace{11mu}{\underset{\_}{H}}^{({k,K_{B},k_{M}})}} \right)}\;\underset{\_}{t}}} \\{{= {{\underset{\_}{H}}^{({k,k_{M}})}\underset{\_}{t}}},{k = {1\mspace{11mu}\ldots\mspace{11mu} K}},{k_{M} = {1\mspace{11mu}\ldots\mspace{11mu}{K_{M}.}}}}\end{matrix} & (5)\end{matrix}$

r ^((k,k) ^(M) ⁾ and H ^((k,k) ^(M) ⁾ have the dimensions (S+W−1)×1 or(S+W−1)×(K_(B)S). The MT and receive-antenna-specific channel foldingmatrix is designated as H ^((k,k) ^(M) ⁾.

The K_(M) signals r ^((k,k) ^(M) ⁾ received at MT μ_(k) k=1 . . . K) of(5) can be arranged in a vector

$\begin{matrix}{{{\underset{\_}{r}}^{(k)} = \left( {{\underset{\_}{r}}^{{({k,1})}^{T}}\mspace{11mu}\ldots\mspace{11mu}{\underset{\_}{r}}^{{({k,K_{M}})}^{T}}} \right)^{T}},{k = {1\mspace{11mu}\ldots\mspace{11mu} K}},} & (6)\end{matrix}$of dimension K_(M)(S+W−1) which is designated as the MT-specific receivesignal at MT μ_(k).

With the [K_(M)(S+W−1)]×(K_(B)S) MT-specific channel folding matrices

$\begin{matrix}{{{\underset{\_}{H}}^{(k)} = \left( {{\underset{\_}{H}}^{{({k,1})}^{T}}\mspace{11mu}\ldots\mspace{11mu}{\underset{\_}{H}}^{{({k,K_{M}})}^{T}}} \right)^{T}},{k = {1\mspace{11mu}\ldots\mspace{11mu} K}},} & (7)\end{matrix}$the MT-specific receive signal r ^((k)) of (6) becomesr ^((k))=H ^((k)) t.  (8)

The K MT-specific receive signals r ^((k)) of (6) are combined to formthe overall receive signal

$\begin{matrix}\begin{matrix}{\underset{\_}{r} = \left( {{\underset{\_}{r}}^{{(1)}^{T}}\mspace{11mu}\ldots\mspace{11mu}{\underset{\_}{r}}^{{(K)}^{T}}} \right)^{T}} \\{= \underset{\underset{\_}{H}}{\underset{︸}{\left( {{\underset{\_}{H}}^{{(1)}^{T}}\mspace{11mu}\ldots\mspace{11mu}{\underset{\_}{H}}^{{(K)}^{T}}} \right)^{T}}\underset{\_}{t}}} \\{= {\underset{\_}{H}\underset{\_}{t}}}\end{matrix} & (9)\end{matrix}$

r and H from (9) have the dimensions KK_(M)(S+W−1) or[KK_(M)(S+W−1)]×(K_(B)S) respectively.

Data Transmission and Recognition

It is assumed that in a TDMA burst, N data symbols are to be transmittedfrom the AP to the MT μ_(k) k=1 . . . K). The d _(n) ^(k)), k=1 . . . Nintended for MT μ_(k), k=1 . . . K are assigned in the data vector

$\begin{matrix}{{\underset{\_}{d}}^{(k)} = \left( {{\underset{\_}{d}}_{1}^{(k)}\mspace{11mu}\ldots\mspace{11mu}{\underset{\_}{d}}_{N}^{(k)}} \right)^{T}} & (10)\end{matrix}$the dimension N. The K data vectors d ^(k)) (k=1 . . . K) are combinedto form the overall data vector

$\begin{matrix}{\underset{\_}{d} = {\left( {{\underset{\_}{d}}^{{(1)}^{T}}\mspace{11mu}\ldots\mspace{11mu}{\underset{\_}{d}}^{{(K)}^{T}}} \right)^{T} = \left( {{\underset{\_}{d}}_{1}\mspace{11mu}\ldots\mspace{11mu}{\underset{\_}{d}}_{KN}} \right)^{T}}} & (11)\end{matrix}$of dimension KN. To transmit data from the AP to the MT, the overalltransmit signal t of (3) must be expressed by the overall data vector dof (11). If linear modulation is assumed, the modulation process can beexpressed ast=Md.  (12)

The matrix M is called the modulator matrix and has the dimension(K_(B)S)×(KN).

According to the observations made in [3], for each K MT μ_(k) k=1 . . .K) a demodulator matrix D ^((k)) of dimension N×[K_(M)(S+W−1)] must bedefined in advance and the overall demodulator matrix of the dimension(KN)×[KK_(M)(S+W−1)] is then specified asD=diagonal block matrix (D ⁽¹⁾ . . . D ^((k)))  (13)

FIG. 1 shows the system model of the MIMO-JT method. In the case of theJT, the modulator matrix M of (12) is determined taking into account thedemodulator matrix D of (13) and the channel folding matrix H of (9) aposteriori, such that

$\begin{matrix}{\underset{\_}{d}\overset{j}{=}{{\underset{\_}{D}\underset{\_}{r}} = {{\underset{\_}{D}\underset{\_}{H}\underset{\_}{t}} = {\underset{\_}{D}\underset{\_}{H}\underset{\_}{M}\underset{\_}{d}}}}} & (14)\end{matrix}$applies. According to the representation in [1, 2, 3] one selectionoption is

$\begin{matrix}{\underset{\_}{M} = {\left( {\underset{\_}{D}\mspace{11mu}\underset{\_}{H}} \right)^{*T}{\left( {\underset{\_}{D}\mspace{11mu}{\underset{\_}{H}\left( {\underset{\_}{D}\mspace{11mu}\underset{\_}{H}} \right)}^{*T}} \right)^{- 1}.}}} & (15)\end{matrix}$

In this case, for a given H and D the overall transmit energy ∥t∥²/2 isminimized. A major problem in designing this type of MIMO-JT method isthat of defining the demodulator matrix D in order to obtain anadvantageous system performance.

To aid clarity, a MIMO system with only one subscriber is consideredbelow.

In the investigations of JT systems conducted thus far, multipleantennas have only been taken into account at the transmit station (AP)and not at the receiver stations (MT), wherein MIMO antenna arrangementsare not included in the considerations. The important point whenincluding these types of antenna arrangements in JT systems is thedefinition of a suitable demodulator matrix.

Elementary JT System with One MIMO Antenna Arrangement

In this section, an elementary JT system is considered, in which the APcommunicates with just one MT μ_(k), kε(1 . . . K) from a collective ofK MT μ_(k) (k=1 . . . K) and in which an individual data symbol istransmitted to this MT. This situation with just one MT and just onedata symbol is indicated below by the index “0”.

The MIMO antenna arrangement considered consists of KB transmit antennasat the AP and K_(M) receive antennas at each MT μ_(k) (k=1 . . . K). Thenames and dimensions of the vectors and matrices introduced in thecourse of this section are summarized in Tables 1 and 2.

In each of the K_(B) transmit antennas the transmit antenna-specifictransmit signal

$\begin{matrix}{{{\underset{\_}{t}}_{0}^{({k,k_{B}})} = \left( {{\underset{\_}{t}}_{0,1}^{({k,k_{B}})}\mspace{11mu}\ldots\mspace{11mu}{\underset{\_}{t}}_{0,S_{0}}^{({k,k_{B}})}} \right)^{T}},{k_{B} = {1\mspace{11mu}\ldots\mspace{11mu} K_{B}}},} & (16)\end{matrix}$of dimension S₀ is injected. If S₀ is greater than 1, the transmitteddata symbol is spread spectrally. S₀ is thus called the spread factor.The K_(B) antenna-specific transmit signals t ₀ ^(k,k) ^(B) ⁾ of (16)are combined into the overall transmit signal

$\begin{matrix}{{\underset{\_}{t}}_{0}^{(k)} = \left( {{\underset{\_}{t}}_{0}^{{({k,1})}^{T}}\mspace{11mu}\ldots\mspace{11mu}{\underset{\_}{t}}_{0}^{{({k,K_{B}})}^{T}}} \right)^{T}} & (17)\end{matrix}$of dimension K_(B)S₀.

The radio channel between the transmit antenna k_(B) and the receiveantenna k_(M) of the MT μ_(k) is characterized by the channel responseword

$\begin{matrix}{{\underset{\_}{h}}^{({k,k_{B},k_{M}})} = \left( {{\underset{\_}{h}}_{1}^{({k,k_{B},k_{M}})}\mspace{11mu}\ldots\mspace{11mu}{\underset{\_}{h}}_{W}^{({k,k_{B},k_{M}})}} \right)^{T}} & (18)\end{matrix}$of the dimension W. With h ^((k,k) ^(B) ^(,k) ^(M) ⁾ from (18) the MT-and antenna-specific channel matrix

$\begin{matrix}{{{\underset{\_}{H}}_{0}^{({k,k_{B},k_{M}})} = \left( {\underset{\_}{H}}_{{0\mspace{11mu} i},j}^{({k,k_{B},k_{M}})} \right)},{i = {{1\mspace{11mu}\ldots\mspace{11mu} S_{0}} + W - 1}},{j = {1\mspace{11mu}\ldots\mspace{11mu} S_{0}}},{{\underset{\_}{H}}_{{0\mspace{11mu} i},j}^{({k,k_{B},k_{M}})} = \left\{ {{{\begin{matrix}{\underset{\_}{h}}_{i - j + 1}^{({k,k_{B},k_{M}})} & {{1 \leq {i - j + 1} \leq W},} \\0 & {{sonst},}\end{matrix}k_{M}} = {1\mspace{11mu}\ldots\mspace{11mu} K_{M}}},{k = {1\mspace{11mu}\ldots\mspace{11mu} K}},{k_{B} = {1\mspace{11mu}\ldots\mspace{11mu} K_{B}}},} \right.}} & (19)\end{matrix}$can be formed. H₀ ^((k,k) ^(B) ^(,k) ^(M) ⁾ has the dimension(S₀+W−1)×S₀.

With t ₀ ^((k)) of (17) and H₀ ^((k,k) ^(B) ^(,k) ^(M) ⁾ of (19) thesignal received at the receive antenna k_(M) of MT μk can be expressedas a vector

$\begin{matrix}\begin{matrix}{{\underset{\_}{r}}_{0}^{({k,k_{M}})} = {\sum\limits_{k_{B} = 1}^{K_{B}}{{\underset{\_}{H}}_{0}^{({k,k_{B},k_{M}})}{\underset{\_}{t}}_{0}^{({k,k_{B}})}}}} \\{{= {\underset{{\underset{\_}{H}}_{0}^{({k,k_{M}})}}{\underset{︸}{\left( {{\underset{\_}{H}}_{0}^{({k,1,k_{M}})}\mspace{11mu}\ldots\mspace{11mu}{\underset{\_}{H}}_{0}^{({k,K_{B},k_{M}})}} \right)}}{\underset{\_}{t}}_{0}^{(k)}}},{k_{M} = {1\mspace{11mu}\ldots\mspace{11mu} K_{M}}},}\end{matrix} & (20)\end{matrix}$of dimension S₀+W−1. H₀ ^((k,k) ^(M) ⁾ in (20) has the dimension(S0+W−1)×(K_(B)S₀). r ₀ ^((k,k) ^(M) ⁾ of (20) is an MT- and receiveantenna-specific signal. With r ₀ ^((k,k) ^(M) ⁾ the overall signalreceived at MT μ_(k) is received as

$\begin{matrix}\begin{matrix}{{\underset{\_}{r}}_{0}^{(k)} = \left( {{\underset{\_}{r}}_{0}^{{({k,1})}^{T}}\mspace{11mu}\ldots\mspace{11mu}{\underset{\_}{r}}_{0}^{{({k,K_{M}})}^{T}}} \right)^{T}} \\{= {\underset{{\underset{-}{H}}_{0}^{(k)}}{\underset{︸}{\left( {{\underset{\_}{H}}_{0}^{{({k,1})}^{T}}\mspace{11mu}\ldots\mspace{11mu}{\underset{\_}{H}}_{0}^{{({k,K_{M}})}^{T}}} \right)^{T}}}{\underset{\_}{t}}_{0}^{(k)}}} \\{= {{\underset{\_}{H}}_{0}^{(k)}{\underset{\_}{t}}_{0}^{(k)}}}\end{matrix} & (21)\end{matrix}$

r ₀ ^(k)) and H₀ ^(k)) from (21) have the dimensions K_(M) (S₀+W−1) or[_(KM)(S₀+W−1)×(K_(B)S₀). FIG. 2 shows the structure of the matrix H₀^(k)).

With t ₀ ^(k)) from (2) and r ₀ ^(k)) from (21), the energiestransmitted by the AP and received by MT μ_(k) become

$\begin{matrix}{T_{0}^{(k)} = {{\underset{\_}{t}}_{0}^{{(k)}^{*T}}{\underset{\_}{t}}_{0}^{(k)}\mspace{14mu}{or}}} & (22) \\\begin{matrix}{R_{0}^{(k)} = {{\underset{\_}{r}}_{0}^{{(k)}^{*T}}{\underset{\_}{r}}_{0}^{(k)}}} \\{= {{\underset{\_}{t}}_{0}^{{(k)}^{*T}}{\underset{\_}{H}}_{0}^{{(k)}^{*T}}{\underset{\_}{H}}_{0}^{(k)}{{\underset{\_}{t}}_{0}^{(k)}.}}}\end{matrix} & (23)\end{matrix}$

One would also require that the ratio R ₀ ^(k))/T₀ ^(k)) f R ₀ ^(k))from (23) and T₀ ^(k)) from (22) is to be maximized by the correctchoice of t ₀ ^(k)) from (17). To achieve this maximization, t ₀ ^(k))from (17) should be selected as follows:

$\begin{matrix}{{{\underset{\_}{t}}_{0}^{(k)} = {\arg\;{\max\limits_{{\underset{\_}{t}}_{0}^{(k)}}\left( \frac{{\underset{\_}{t}}_{0}^{{(k)}^{*T}}{\underset{\_}{H}}_{0}^{{(k)}^{*T}}{\underset{\_}{H}}_{0}^{(k)}{\underset{\_}{t}}_{0}^{(k)}}{{\underset{\_}{t}}_{0}^{{(k)}^{*T}}{\underset{\_}{t}}_{0}^{(k)}} \right)}}},} & (24)\end{matrix}$which corresponds to a Rayleigh quotient. With H₀ ^(k)) from (21) thetransmit signal t ₀ ^(k)) determined by (24) is the inherent vector u₀^(k)) of the matrix H₀ ^(k)r) with H₀ ^(k)) belonging to the largestinherent value of this matrix, meaningt ₀ ^((k))=u ₀ ^((k)).  (25)

By substitution of t ₀ ^(k)) from (25) in (21) the overall receivesignalr ₀ ^((k))=H ₀ ^((k))u₀ ^((k)).  (26)is produced.

The best demodulator for this signal is a filter adapted to the signal,which with r ₀ ^(k)) from (21), leads to the demodulator matrix

$\begin{matrix}\begin{matrix}{{\underset{\_}{D}}_{0}^{(k)} = {\underset{\_}{r}}_{0}^{{(k)}^{*T}}} \\{= {{\underset{\_}{u}}_{0}^{{(k)}^{*T}}{\underset{\_}{H}}_{0}^{{(k)}^{*T}}}} \\{= \left( {{\underset{\_}{D}}_{0}^{({k,1})}\mspace{11mu}\ldots\mspace{11mu}{\underset{\_}{D}}_{0}^{({k,K_{M}})}} \right)}\end{matrix} & (27) \\{\mspace{45mu}{= \left( {{\underset{\_}{D}}_{0,1}^{(k)}\mspace{11mu}\ldots\mspace{11mu}{\underset{\_}{D}}_{0,{K_{M}{({S_{0} + W - 1})}}}^{(k)}} \right)}} & (28)\end{matrix}$of dimension 1×[K_(M)(S₀+W−1)], where the receive antenna-specificdemodulator matrices

$\begin{matrix}{{{\underset{\_}{D}}_{o}^{({k,k_{M}})} = {\underset{\_}{\tau}}_{0}^{{({k,k_{M}})}*T}},{k_{M} = {1\mspace{11mu}\ldots\mspace{11mu} K_{M}}},} & (29)\end{matrix}$have the dimension 1×(S₀+W−1).Multiple MT-JT System with a Number of Symbols with One MIMO AntennaArrangement

a) Transmission Model

If we now look at the more realistic situation in which the APcommunicates simultaneously with all K MT μ_(k) (k=1 . . . K) and where,instead of only one data symbol per MT, N>1 data symbols aretransmitted, with each of these data symbols being spectrally spread bythe factor S₀ already introduced in Section 2.

TABLE 1 Names and dimensions of vectors introduced in Section 2. VectorName Dimension t ₀ ^(k,k) ^(B) ⁾ MT- and transmit antenna- S₀ Specifictransmit signal t ₀ ^(k)) MT-specific transmit signal K_(B)S₀ h ^((k,k)^(B) ^(,k) ^(M) ⁾ MT- and antenna-specific W Channel response word r ₀^(k,k) ^(B) ⁾ MT- and receive antenna- S₀ + W − 1 Specific receivesignal r ₀ ^(k)) MT-specific K_(M)(S + W − 1) Receive signal u ₀ ^(k))Inherent vector of K_(B)S₀ H ^(k)*τ) H ^(k)) belonging to the largestinherent value

TABLE 2 Names and dimensions of matrices introduced in Section 2. MatrixName Dimension H ₀ ^(k,k) ^(B) ^(,k) ^(M) ⁾ MT- and antenna- (S₀ + W− 1) × S0 specific channel matrix H ₀ ^(k,k) ^(M) ⁾ MT- and receive(S₀ + W − 1) × (K_(B)S₀) antenna-specific channel matrix H ₀ ^(k))MT-specific [K_(M) (S₀ + W − 1)] × (K_(B)S₀) channel matrix D ₀ ^(k))MT-specific 1 × [K_(M) (S₀ + W − 1)] demodulator matrix D ₀ ^(k,k) ^(M)⁾ MT- and receive 1 × (S₀ + W − 1) antenna specific demodulator matrix

As before, the AP is equipped with KB transmit antennas and each MTμ_(k) features K_(M) receive antennas. Below, the signal descriptionsintroduced in Section 2 are first adapted to this new situation. Then,on the basis of the demodulator matrices D ₀ ^(k)) from (27) ademodulator matrix D is created. The names and dimensions of the vectorsand matrices introduced in the course of Section 3 are summarized inTables 3 or 4.

Instead of t ₀ ^(k,k) ^(B) ⁾ from (16) there is the transmitantenna-specific transmit signal

$\begin{matrix}{{{\underset{\_}{t}}^{(k_{B})} = \left( {{\underset{\_}{t}}_{1}^{(k_{B})}\mspace{11mu}\ldots\mspace{11mu} t_{S}^{(k_{B})}} \right)^{T}},{k_{B} = {1\mspace{11mu}\ldots\mspace{11mu} K_{B}}},} & (30)\end{matrix}$of the dimensionS=NS₀,  (31)and instead of t ₀ ^(k)) from (17) the overall transmit signal

$\begin{matrix}{\underset{\_}{t} = \left( {{\underset{\_}{t}}^{{(1)}^{T}}\ldots\mspace{11mu}{{\underset{\_}{t}}^{(K_{B})}}^{T}} \right)^{T}} & (32)\end{matrix}$of the dimension K_(B)S is produced.

Instead of H ₀ ^(k,k) ^(B) ^(,k) ^(M) ⁾ from (19) the MT- andantenna-specific channel matrix

$\begin{matrix}{{{\underset{\_}{H}}^{({k,k_{B},k_{M}})} = \left( {\underset{\_}{H}}_{i,j}^{({k,k_{B},k_{M}})} \right)},{i = {{1\mspace{11mu}\ldots\mspace{11mu} S} + W - 1}},{j = {1\mspace{11mu}\ldots\mspace{11mu} S}},{{\underset{\_}{H}}_{i,j}^{({k,k_{B},k_{M}})} = \left\{ {{{\begin{matrix}{\underset{\_}{h}}_{i - j + 1}^{({k,k_{B},k_{M}})} & {{1 \leq {i - j + 1} \leq W},} \\0 & {{sonst},}\end{matrix}k_{M}} = {1\mspace{11mu}\ldots\mspace{11mu} K_{M}}},{k = {1\mspace{11mu}\ldots\mspace{11mu} K}},{k_{B} = {1\mspace{11mu}\ldots\mspace{11mu}{K_{B}.}}}} \right.}} & (33)\end{matrix}$is produced.

H ₀ ^(k,k) ^(B) ^(,k) ^(M) ⁾ from (33) has the dimension (S+W−1)×S.

Instead of r ₀ ^(k,k) ^(B) ⁾ from (20), t from (32) and H ₀ ^(k,k) ^(B)^(,k) ^(M) ⁾ from (33) produce the MT- and receive antenna-specificreceive signal

$\begin{matrix}{{\underset{\_}{r}}^{({k,k_{M}})} = {{\sum\limits_{k_{B} = 1}^{K_{B}}\;{{\underset{\_}{H}}^{({k,k_{B},k_{M}})}{\underset{\_}{t}}^{(k_{B})}}}\mspace{65mu} = {\underset{\underset{{\underset{\_}{H}\;}^{({k,k_{M}})}}{︸}}{\left( {{\underset{\_}{H}}^{({k,1,k_{M}})}\mspace{11mu}\ldots\mspace{11mu}{\underset{\_}{H}}^{({k,K_{B},k_{M}})}} \right)}{\underset{\_}{t}.}}}} & (34)\end{matrix}$

r ^(k,k) ^(B) ⁾ and H ^(k,k) ^(M) ⁾ from (34) have the dimensions(S+W−1) or (S+W−1)×(K_(B)S).

With H ^(k,k) ^(M) ⁾ from (34) and t from (32) the overall signalreceived by MT μk can be written as follows:

$\begin{matrix}{{\underset{\_}{r}}^{(k)} = {\left( \;{{{\underset{\_}{r}}^{({k,1})}}^{T}\mspace{11mu}\ldots\mspace{11mu}{{\underset{\_}{r}}^{({k,K_{M}})}}^{T}} \right)^{T}\mspace{34mu} = {\underset{{\underset{\_}{H}\;}^{(k)}}{\underset{︸}{\left( {{\underset{\_}{H}}^{{({k,1})}^{T}}\mspace{11mu}\ldots\mspace{11mu}{{\underset{\_}{H}}^{({k,k_{M}})}}^{T}} \right)}\underset{\_}{t}}\mspace{11mu}\mspace{34mu} = {\underset{\_}{H^{(k)}}\;\underset{\_}{t}}}}} & (35)\end{matrix}$

r ^(k)) and H ^(k)) from (35) have the dimensions K_(M)(S+W−1) or[K_(M)(S+W−1)]×K_(B)S. As an extension of the observations in theprevious section, an overall receive signal

$\begin{matrix}{\underset{\_}{r} = {\left( \;{{{\underset{\_}{r}}^{(1)}}^{T}\mspace{11mu}\ldots\mspace{11mu}{{\underset{\_}{r}}^{(K)}}^{T}} \right)^{T}\mspace{11mu} = {\left( {{\underset{\_}{H}}^{{(1)}^{T}}\mspace{11mu}\ldots\mspace{11mu}{{\underset{\_}{H}}^{(K)}}^{T}} \right)^{T}\mspace{11mu}\mspace{11mu} = {\underset{\_}{H}\underset{\_}{t}}}}} & (36)\end{matrix}$is now introduced with the K receive signals r ^(k)) from (34) of all KMT μ_(k) (k=1 . . . K). r and H from (35) have the dimensionsKK_(M)(S+W−1) or [KK_(M)(S+W−1)]×K_(B)S.

b) Determining the Demodulator Matrix D

According to the observations made in [2], for each of the K MT μ_(k)(k=1 . . . K) a demodulator matrix D ^(k)) of dimension N×[K_(M)(S+W−1)]must be determined and then the overall demodulator matrix of thedimension (KN)×[KK_(M)(S+W−1)] is produced asD=diagonal block matrix (D ⁽¹⁾ . . . D ^((k)))  (37)

TABLE 3 Names and dimensions of vectors introduced in this sectionVector Name Dimension t ^(k) ^(a) ⁾ transmit antenna-specific transmit S= NS₀ signal t Overall transmit signal KBS r ^(k,k) ^(a) ⁾ MT- andreceive antenna specific S + W − 1 receive signal r ^(k)) MT-specificreceive signal K_(M)(S + W − 1) r Overall receive signal KK_(M)(S + W− 1) d Overall data vector KN

TABLE 4 Names and dimensions of matrices introduced in this section.Matrix Designation Dimension H ^(k,k) ^(a) ^(,k) ^(M) ^() H) MT- andantenna- (S + W − 1) × S specific channel matrix H ₀ ^(k,k) ^(M) ⁾ MT-and receive (S + W − 1) × (K_(B)S) antenna-specific channel matrix H^(k)) MT-specific [Km (S + W − 1) ] × (K_(B)S) channel matrix H Overallchannel [KK_(M)(S + W − 1) ] × (K_(B)S) matrix D ^(k)) MT-specific N ×[K_(M)(S + W − 1) demodulator matrix D Overall (KN) × [KK_(M)(S + W − 1)] demodulator matrix B System matrix (KN) × (K_(B)S) M Modulator matrix(K_(B)S) × (KN)

The decisive point of the proposal for constructing the demodulatormatrix D ^((k)) taking into consideration the channel characteristicslies in the demodulator matrix D₀ ^(k)) introduced in (27). The N linesof D ^((k)) are obtained as shifted versions of D₀ ^(k)) from (27) inaccordance with the method

$\begin{matrix}{{{\underset{\_}{D}}_{i,j}^{(k)} = \left( {\underset{\_}{D}}_{i,j}^{(k)} \right)},{i = {1\mspace{11mu}\ldots\mspace{11mu} N}},{j = {1\mspace{11mu}{\ldots\mspace{11mu}\left\lbrack {K_{M}\left( {{S_{0}N} + W - 1} \right)} \right\rbrack}}},{{\underset{\_}{D}}_{i,j}^{(k)} = \left\{ {\begin{matrix}{\underset{\_}{D}}_{0,p}^{(k)} & {{1 \leq {\left( {j - {\left( {i - 1} \right)S_{0}}} \right){mod}\;\left( {{S_{0}N} + W - 1} \right)} \leq {S_{0} + W - 1}},} \\0 & {{sonst},}\end{matrix}{with}} \right.}} & (38) \\{{p = {{\left( {j - {\left( {i - 1} \right)S_{0}}} \right){{mod}\left( {{S_{0}N} + W - 1} \right)}} + {\left( {S_{0} + W - 1} \right) \cdot \left\lbrack \frac{j}{{S_{0}N} + W - 1} \right\rbrack}}},} & (39)\end{matrix}$and [ ] designating the integer part. The structure of D ^((k)) from(38) is shown in FIG. 3.

D from (37) can be formed with the K matrices D ^((k)) from (38). With Dfrom (37) and H from (36) the system matrixB=DH  (40)of the dimension KN×K_(B)S is obtained. As shown in [2], the overalltransmit signal t from (22) and the overall data vector d [2] of thedimension KN can be obtained as

$\begin{matrix}{t = {{\underset{\underset{\_}{M}\;}{\underset{︸}{{B^{*T}\left( {\underset{\_}{BB}}^{*T} \right)}^{- 1}}}\underset{\_}{d}}\; = {\underset{\_}{M}\;\underset{\_}{d}}}} & (41)\end{matrix}$with the modulator matrix M from (41) possessing the dimension(K_(B)S)×(KN).

Although the present invention has been described with reference tospecific embodiments, those of skill in the art will recognize thatchanges may be made thereto without departing from the spirit and scopeof the present invention as set forth in the hereafter appended claims.

1. A method of transmitting information in a radio communication system, the method comprising: connecting a transmit station to at least two receiver stations via a radio communication interface; including a transmit antenna with at least two antenna elements at the transmit station and including a transmit antenna with at least two antenna elements at each of the receiver stations, wherein the transmit station and the receiver stations communicate using MIMO transmission; generating transmit signals for radiation from the antenna elements of the transmit antenna of the transmit station in a common process and matching the transmit signals with regards to a transmit energy to be used for radiation; detecting received signals received by antenna elements of receive antennas of the receiver stations in a linear signal processing through demodulation, taking into account space and time transmission characteristics between the transmit station and the respective receiver stations, wherein a receiver station specific transmit signal corresponds to a Rayleigh quotient; calculating individual transmit signals for the antenna elements of the transmit antenna of the transmit station before radiation using a modulator matrix; generating a transmit signal vector using a linear modulation of a data vector to be transmitted with the modulator matrix; processing the received signals, the processing including using a demodulation matrix for linear receive-side signal processing; connecting the transmit station to the receiver stations using at least one radio channel having a channel matrix; and including a system matrix in the modulator matrix specified by a product of the demodulator matrix and the channel matrix.
 2. A radio communication system for transmitting information, comprising: at least one transmit station including a transmit antenna with at least two antenna elements; at least two receiver stations each including a transmit antenna with at least two antenna elements; and a radio communication interface for connecting the at least one transmit station and the at least two receiver stations; wherein the transmit station generates transmit signals which are radiated by the antenna elements of the transmit antenna of the transmit station in a common process and matches the transmit signals with regards to a transmit energy to be employed for radiation; wherein each of the receiver stations detect receive signals received by antenna elements of receive antennas of the receiver stations in a linear signal processing through demodulation, taking into account space and time transmission characteristics between the transmit station and the respective receiver stations; wherein a receiver station specific transmit signal corresponds to a Rayleigh quotient; wherein individual transmit signals are calculated for the antenna elements of the transmit antenna of the transmit station before radiation using a modulator matrix; wherein a transmit signal vector is generated using a linear modulation of a data vector to be transmitted with the modulator matrix; wherein the received signals are processed using a demodulation matrix for linear receive-side signal processing; wherein the transmit station and the receiver stations are connected using at least one radio channel having a channel matrix; and wherein a system matrix is included in the modulator matrix as specified by a product of the demodulator matrix and the channel matrix. 